Question

What is compressibility?

Answer 1

In order to answer this question, first we will go through the whole concept or the explanation of compressibility with their suitable expression and then we will also discuss the compressibility of other states such as liquid.

Complete answer:
Compressibility is the property of being compressed by pressure into a smaller space. This feature is caused by porosity, and the change in bulk is caused by the pressure bringing the particles closer together.
The compressibility of a fluid is essentially a measurement of the change in density that a given change in pressure will cause in the fluid. Gases, on the other hand, are highly compressible, whereas most liquids are not.
Compressibility effects can have a significant impact on fluid flow. Compressible fluid flow, often known as gas dynamics, is the study of these flows in which density and temperature variations are significant.
Or in other words, the compressibility (also known as the coefficient of compressibility or, if the temperature is held constant, the isothermal compressibility) is a measure of a fluid or solid relative volume change as a response to a pressure (or mean stress) shift in thermodynamics and fluid mechanics.
In its simple form, the compressibility $k$ (denoted $\beta$ in some fields) may be expressed as:
$\kappa = - \dfrac{1}{V}\dfrac{{\partial V}}{{\partial p}}$
where, $V$ is the volume
$p$ is the pressure.
The choice to define compressibility as the negative of the fraction makes compressibility positive in the (usual) case that an increase in pressure induces a reduction in volume. The reciprocal of compressibility at fixed temperature is called the isothermal bulk modulus.

Note:
Compressibility is a quality or state of being compressible. The fractional change in volume to the stress applied to a body is equal to the reciprocal of the bulk modulus.
The measure of a liquid's relative volume change when the pressure acting on it varies is called compressibility. Thermodynamics and fluid mechanics are both connected to compressibility.